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A Russian Pass B1 FET Preamp/Buffer
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Author:  mwhouston [ 18 Oct 2010, 18:34 ]
Post subject:  Re: A Russian Pass B1 FET Preamp/Buffer

What a difference a night makes. Just leaving the preamp over night and running a few extra CD through it has losened-up the bottom end. Bass is back, extended and oh-so tight. It goes as low as the tube preamp.

After some testing, into 10k load: -3dB points 5Hz -> 780kHz.
Max voltage out peak to peak 13V into 10k
Max voltage out peak to peak 8V into 1k
Attachment:
Nelson-Pass-B1-Buffer-100Hz.jpg

Attachment:
Nelson-Pass-B1-Buffer-20kHz.jpg

Because this is a source follower preamp it de-amplifies. It is (as Pass says) and driver more than a preamp. You get out about 85% of what you put in.

Take look at the square wave outputs at 100hz (note the function generator on the top line is also sloped off slightly). The B1's output is the bottom square wave in both images. The square wave at 50khz is still pretty good.

I can only imaging the sound will improve over the next few weeks of play. The mids and treble are very controlled and crystal clear. Siblance is perfect, cymbals very natural. Huge amount of detail is presented. An excellent preamp and an easy build.

Author:  mwhouston [ 30 Oct 2010, 07:47 ]
Post subject:  Re: A Russian Pass B1 FET Preamp/Buffer

My BoZ is completed check the thread: JFET BoZ (Bride of Zen by Nelson Pass). Images and better listening notes to follow.

Author:  mwhouston [ 01 Nov 2010, 05:24 ]
Post subject:  Re: A Russian Pass B1 FET Preamp/Buffer

I have had a chance to compare the Nelson Pass B1 and BoZ, (simple form) both my builds. For absolute sound rawness and detail the B1 is supreme. But of course the B1 has no gain and even has negative gain. Its role is to drive.

Both preamps have the same metal film and carbon resistors from the same store. Both have exactly the same input cap (Russian military 1uf 40y-9, paper in oil (PIO)) and output caps, 100V polypropylene 10uf. With the BoZ this is snubbed by a 0.1uf poly. Hook-up wire varies from cotton coated tinned solid core copper to wire wrap wire (WWW) in BoZ. Both enclosures are Hammond anodised Al cases with the B1 having a slightly longer case. Both preamps have a single jFET the 2SK170 (BL).

The two preamps have been compared with different external power supplies. The B1 a 19V SMPS and BoZ 4 X 9V lithium batteries. You may rightfully argue that in the PS alone there is enough difference to make any sonic comparison redundant. If you do. bow out now, if not read on.

Let’s digress a little. The B1 worked first time it was powered up but BoZ gave me serious attitude. This was my fault due to the fact I added a input cap where there was none. Where I placed it blocked the critical bias voltage for the jFET. But it doesn’t stop there. A 1ohm resistor, in the PS, went open cct. And while re-assembling the case I caught the power wires which shorted the batteries.

Both preamps have good control over the bass. Both extend into low bass. BoZ has greater weight in the bottom end and excellent clarity and detail through the mid range and into treble. But B1 has a rawness of mid-range and treble which reveals a vulnerability in the music which draws you into it. You can’t turn away or stop listening. The B1 connects you with the performance where BoZ places the performance in your listening area.

In conclusion if you need gain and want a very natural, un-coloured sounding, simple preamp, BoZ is for you. If you have 200W of raw power in a power amp and a line driver will suit you better, take the B1 challenge. But you may find its rawness confronting and even distracting.

Remember both preamp invert the phase so if your power amp is non-phase inverting swap you speaker leads over.

Author:  mwhouston [ 01 Nov 2010, 17:28 ]
Post subject:  Re: A Russian Pass B1 FET Preamp/Buffer

The B1's rawness was not only my comment. This was commented on a by small pannel of hard core listeners.

An image of the B1 after engraving.
Attachment:
B1Finishedss.jpg


Image

Author:  mwhouston [ 30 Nov 2010, 19:26 ]
Post subject:  Re: A Russian Pass B1 FET Preamp/Buffer

I fellow DIYer and another member of the Melblourne Audio Club brought around his newly completed Pass F5. The set-up was Oppo BDP-83SE, BoZ, Fostex FE206E in backloaded horn.

We played 6 tracks and then I dropped in the B1 in place of the BoZ. Dave, the F5 owner, swore it was much better than BoZ. I swapped the two preamps in and out and each time he believed the B1 to be better. Once more the "no gain" issues meant some tracks played too quietly but sonically the B1 appears to win out-right.

I have to use BoZ to get the volume I need and even now with my new input capless BoZSE I still think the B1 sonically better. One other audio club member agreed but on my system only. The BoZ I made for a friend, also from the audio club, claims BoZ comparable to his $3500 Audio Note tube preamp. He liked BoZ over the B1. Go figure!

Author:  Gio [ 30 Nov 2010, 20:03 ]
Post subject:  Re: A Russian Pass B1 FET Preamp/Buffer

Hey Mark,

How did the F5 do with the FE206E BLH compared with your other amps? I'll have to find some time to put together the F5 as I have all the parts.

Cheers

Author:  mwhouston [ 30 Nov 2010, 22:59 ]
Post subject:  Re: A Russian Pass B1 FET Preamp/Buffer

Gio wrote:
How did the F5 do with the FE206E BLH compared with your other amps? I'll have to find some time to put together the F5 as I have all the parts.

I hate to admit it Dave has finally built a good SS amp. I haven't had a look at the schematic yet but it did sound excellent. If I didn't have my SET and just had an F5 I'd probably not look for anything else. In fact it may have been better than my SET of the short time we listened to it.

He built fully dual mono. So the two channels only share the power cord and case. The rest is totally split. Dave is now building another one.

Author:  dtsup1 [ 30 Nov 2010, 23:04 ]
Post subject:  Re: A Russian Pass B1 FET Preamp/Buffer

Omg...you and Gio are tempting me to continue building my Pass F5 ! :eek:
Alright Gio, build it soon !!

Based on Mark's listening notes, I will pair it with the B1. My CD player has plenty of drive.

A great project !! F5 + B1

Author:  mwhouston [ 01 Dec 2010, 00:35 ]
Post subject:  Re: A Russian Pass B1 FET Preamp/Buffer

Dinesh - did you build the simple BoZ?? And you could build the capless BoZSE 'cause your CD player will have output caps.

You may find just not enough Vol. on some CDs. BoZSE ensure you have losts of gain if nothing else. I may have a BoZ with PS comming up. I'd be ;ooking for parts cost only. It has the Russian PIOs upfront. I could put a shorting pin on these which you could pull if a capped input is required. In some areas I could upgrade it to the SE.

But sounds like you are in build mode I wouldn't want to spoil that.

Author:  dtsup1 [ 01 Dec 2010, 01:08 ]
Post subject:  Re: A Russian Pass B1 FET Preamp/Buffer

Hi Mark,

Which is the simple BoZ ? Can you provide a link? thx..

My CD player has an output cap but I often switch between another source as well (Mede8er HD player) and that does not have an output cap, so I'll have to add the input cap for the BoZ. Also, this will be used with the Aussie Amps Nxv200 (as you have built them as a poweramp). The Aussie amps does not have an input cap, so my BoZ must have the input and output caps.

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